T&T: Bleach in potable tanks

[Ron Nelson]

This comment led me to a question I have re the amount of bleach needed
first to purify and then sustain potable water tanks.  What  concentration to
'shock' it?  And then I assume it would be best to  flush and dilute to a
certain
level?  I can stand a little more than normal  because I have a UV/charcoal
filter for drinking water.   Thanks.
=========================================================

The following is from my archives of saved T&T messages.  I didn't write any
of the below and I don't know who did but I hope it helps.
*********************************************************
Amount of Clorox to water

1 gal. (4.5 liters) 2 drops (0.18 ml.)

5 gal. (23 liters) 11 drops (0.9 ml.)

10 gal. (45 liters) 22 drops (1.8 ml.)

50gal. (230 liters) 1 3/4 teaspoons (9 ml)

100 gal. (450 liters) 3 1/2 teaspoons (18 ml)

220 gal. (1000 liters) 8 teaspoons (40 ml)

500 gal. (2200 liters) 6 tablespoons (90 ml)

1000 gal. (4550 liters) 6 1/2 ounces or 12 tablespoons (180 ml.)

Every Six months I fill the tanks and put in one cup of household
bleach diluted in a gallon of water for each 100 gallons.  I fill the
tank and run the water into all lines.  I let this sit for at least two
hours, then drain the tanks, fill again twice and then taste the water.

There will be a slight amount of residual chlorine, but it will
dissipate rapidly.

You can add 4 oz of sodium bicarbonate per one hundred gallons diluted
as above if you wish.

The problem is that if you keep getting foul water, the tank is
contaminated or the water source is contaminated.  I drink the water in
my tanks--why else have tanks?
******* *******************************

Fresh Water System Problems [Fresh water system problems--foul odor or
taste--are typically caused by allowing water to stagnate in the tank
and especially the lines, creating the ideal environment for molds,
fungi and bacteria that thrive in damp dark places. Here's the
recommended method for re-commissioning fresh water systems; this
should be done at least annually:

Fill the water tank with a solution of 1-cup (8 oz) of household bleach
per 10 gallon tank capacity. Turn on every faucet on the boat
(including a deck wash if you have one), and allow the water to run
until what's coming out smells strongly of bleach. Turn off the
faucets, but leave the system pressurized so the solution remains in
the lines.

Let stand overnight-- at least 8 hours--but NO LONGER THAN 24 hours.
Drain through every faucet on the boat (and if you haven't done this in
a while, it's a good idea to remove any diffusion screens from the
faucets, 'cuz what's likely to   come out will clog them). Fill the
tank again with fresh water only, drain again through every faucet on
the boat, repeating till the water runs clean and smells and tastes
clean.

Cleaning out the tank addresses only the least of the problem...most of
the problem occurs in the lines, so it's very important to leave the
system pressurized while the bleach solution is in the tank to keep the
solution in the lines too.

People have expressed concern about using this method to re-commission
aluminum tanks. While bleach (chlorine) IS corrosive, the effect of an
annual or semi-annual "shock treatment" is negligible compared to the
cumulative effect of holding chlorinated city water in the tank for
years. Nevertheless, it's a good idea to mix the total amount of bleach
in a few gallons of water before putting it into either a stainless or
aluminum tank.

To keep the water system cleaner longer, use your fresh water...keep
water flowing through system. The molds, fungi, and bacteria only start
to grow in hoses that aren't being used. Before filling the tank each
time, always let the dock water run for at least 15 minutes first...the
same critters that like the lines on your boat LOVE the dock supply
line and your hose that sit in the warm sun, and you don't want to
transfer water that's been sitting in the dock supply line to your
boat's system. So let the water run long enough to flush out all the
water that's been standing in them so that what goes into your boat is
coming straight from the water main.

Finally, while the molds, fungi and bacteria in onboard water systems
here in the US may not be pleasant, we're dealing only with
aesthetics...water purity isn't an issue here--or in most developed
nations...the water supply has already been purified (unless you're
using well-water). However, when cruising out of the country, it's a
good idea to know what you're putting in your tanks...and if you're in
any doubt, boil all water that's to be drunk or used to wash dishes,
and/or treat each tankful to purify. It's even more important in these
areas to let the water run before putting it in the tank--wash the
boat, whatever it takes...'cuz any harmful bacteria will REALLY
proliferate in water hoses left sitting on the dock.


------------------------------